Rio de Janeiro defied pre-event expectations yesterday when the opening race of the Olympic regatta was sailed in ideal conditions on Guanabara Bay.

And Ireland's Annalise Murphy similarly dispelled expectations of unsuitability for the Brazilian city when she won the opening race of the women's single-handed event in the Laser Radial class.

The breeze was nevertheless challenging as it varied across the course area. But there was little sign of rubbish or other hazards, while the water appeared relatively clean and odour-free.

This was as Murphy expected from her experience of 10 previous visits to the venue on training and pre-Olympic competitions.

She appeared comfortable as she gradually worked her way up the fleet of 37 boats, from eighth place at the start of the 50-minute race, then into third with a leg of the course to spare, then first overall from where she extended her grip on the chasing pack.

Behind her were all the London 2012 medallists who had beaten her in a memorable medal race four years ago.

But this will be a vastly different regatta than four years ago and while her win nails any questions about her ability, the key will be consistency.

Just as her string of race wins earned her a place in the final then, attaining top five or six places here will be critical.

She finished the second race down in 14th to leave her fourth overall while her rivals managed to crack the consistency challenge needed to overcome Rio's notoriously fickle conditions.

But as China's Lijia Xu, the London gold medallist takes an early overall lead in the class, Murphy was taking a calm but pleased view of her first day.

"It's really tricky, a lot of pressure differences across the course and the wind is up and down with a strong tide in play but I'm happy enough with my day," she said on arrival ashore.

Two more races are planned for today out of a total of 10 expected before Monday's medal race final.

Ireland's other single-handed sailor also opened his first Games with a strong performance.

Finn Lynch from Carlow placed 14th overall in his men's event where 46 sailors are competing.

Behind him in that race was local hero Robert Scheidt, a multiple medallist and at 43 years old hoping to defy the challenge of the average age of medallists in the class (around 30 years) to secure gold on his home waters.

Lynch went on to place 27th in race two and lies 21st overall after day one.

Ireland's other sailors in the men and women's skiff events begin their regatta on Friday.